Heatsink for actively cooled daughterboard system

ABSTRACT

A heatsink for use with an actively cooled daughterboard system. Plural transverse fins are integrally formed with a base portion. The fins are parallel to one another and orthogonal to the bottom of the base portion. The fins have a constant profile relative to the bottom of the base portion, but the base portion has a central portion that is thicker than its end portions. The thickness of the central portion varies according to a radius. The radius is approximated by step differences in the depths of the fins.

FIELD OF THE INVENTION

This invention relates generally to cooling techniques for electroniccircuitry. More particularly, the invention relates to techniques forcooling electronic components that are mounted on a daughterboard.

BACKGROUND

Computer-related electronic systems are commonly constructed usingmultiple interconnected circuit boards. The largest of these circuitboards is typically called the motherboard. Ancillary circuit boardssuch as CPU cards, memory cards and input/output cards are typicallycalled daughterboards. Sockets are provided on the motherboard forreceiving one or more daughterboards and making appropriate electricalconnections between components mounted on the daughterboards and thosemounted on the motherboard. Such sockets are usually designed so thatthe daughterboards may be easily removed and replaced.

Special thermal management problems are presented bymotherboard/daughterboard systems wherein high heat dissipationcomponents are mounted on the daughterboards. Specifically, it has beenfound that fan-driven heat sinks are necessary to prevent the high heatdissipation components such as CPU chips on the daughterboards fromoverheating.

One example of such a motherboard/daughterboard system is described inthe single edge contact cartridge (“SECC”) packaging specificationspromulgated by Intel Corporation. Referring now to FIG. 1, the packagingspecification for boxed SECC2 processors describes a daughterboard 100on which a CPU is mounted. Daughterboard 100 is adapted to engage asocket 102 on a motherboard 104 so that daughterboard 100 is orientedsubstantially perpendicular to motherboard 104. A heatsink 106 isdisposed on one side of daughterboard 100 between the CPU and a fan 108.On the opposite side of daughterboard 100, an SECC2 cover plate 110 isprovided to help anchor heatsink 106 to daughterboard 100. Heatsink 106is generally rectangular and includes plural elongate fins 112. Each offins 112 lies on a plane that is substantially parallel to motherboard104. The axis of rotation of fan 108 is also substantially parallel tomotherboard 104. A fan shroud 114 is provided to direct air flow throughheatsink 106 from the ends of fins 110 to the middle of fins 110 underfan 108 as shown in FIG. 2.

Heatsink 106 also includes tabs 116 on either end. (Tabs 116 are bestillustrated in FIG. 3.) Each of tabs 116 defines a notch 118 forengaging a retaining member of socket 102. An example of such aretaining member is universal retention mechanism 400 (“URM”) shown inFIG. 4. URM 400 includes a frame with top surfaces 406 and a resilientarm 402. Resilient arm 402 includes retaining ledges 404. Typically, oneURM 400 is disposed on each end of socket 102 with its retaining ledges404 facing inward toward the socket. When daughterboard 100 is pushedinto socket 102, notches 118 on either side of heatsink 106 engage theunderside of ledges 404, thereby helping to retain daughterboard 100 insocket 102.

SUMMARY OF THE INVENTION

A heatsink for use with a daughterboard system may include pluraltransverse fins integrally formed with a base portion. The fins areparallel to one another, but are orthogonal relative to the bottom ofthe base portion. The fins have a constant profile relative to thebottom of the base portion, but the base portion has a central portionthat is thicker than its end portions. The thickness of the centralportion varies according to a radius. The radius is approximated by stepdifferences in the depths of the fins.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an actively-cooled daughterboard systemaccording to the prior art.

FIG. 2 is an oblique view of the daughterboard system of FIG. 1.

FIG. 3 is a top plan view of the daughterboard system of FIG. 1.

FIG. 4 is an oblique view of a daughterboard retaining mechanismaccording to the prior art.

FIG. 5 is an oblique view of an actively cooled daughterboard system foroptional use with a heatsink according to a preferred embodiment of theinvention.

FIGS. 6, 7 and 8 are oblique, side and top plan views, respectively, ofthe fan shroud of FIG. 5.

FIGS. 9 and 10 are exploded and assembled side views, respectively, ofthe daughterboard system of FIG. 5.

FIG. 11 is an oblique view of the daughterboard system of FIG. 5 housedin a host computer chassis according to a preferred embodiment of theinvention.

FIGS. 12, 13 and 14 are oblique, side and top plan views, respectively,of a first heatsink for optional use with the daughterboard system ofFIG. 5.

FIG. 15 is an oblique view of a heatsink mounting pin.

FIGS. 16, 17 and 18 are oblique, side and top plan views, respectively,of a second heatsink according to a preferred embodiment of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Actively cooled daughterboard system. FIG. 5 illustrates an activelycooled daughterboard system 500. In daughterboard system 500, one ormore daughterboards are housed inside a fan shroud 600. (In theembodiment shown, two daughterboards are so housed.) Each daughterboardhoused within shroud 600 has a heat generating component such as a CPUmounted on it, and each daughterboard assembly includes a heatsink thatis thermally coupled to the heat generating component. Preferably, eachheatsink includes a plurality of transverse fins (to be furtherdescribed below) oriented so that air may pass between the fms in adirection generally parallel to the plane of the associateddaughterboard. Active cooling is provided by a single fan 700 mounted onthe top of shroud 600 as shown. Using a single fan in this mannereliminates the need for multiple fans located on the individualdaughterboard assemblies.

Fan shroud 600 is illustrated in more detail in FIGS. 6-8. Fan shroud600 has openings 602 in both sides 604 and openings 606 in both ends608. In addition, there is an opening 610 in top surface 612 underneaththe footprint of fan 700. The purpose of openings 602, 604 and 610 is todirect air flow through the plural transverse fins of the heatsinks andthrough fan 700. Preferably, fan 700 is mounted on shroud 600 as shownin FIGS. 7 and 8 so that the axis of rotation of fan 700 issubstantially parallel with planes of the daughterboards (and thus alsoparallel with the outer ends of the transverse fins of the heatsinks).When fan 700 is so oriented, air flow will occur generally in thedirection indicated by arrows 702 (side intake, top effluent) and 802(end intake, top effluent). In alternative embodiments, the direction ofthe airflow may be reversed by changing the blow direction of fan 700.

In the embodiment shown, fan shroud 600 was constructed from a singlesheet of aluminum alloy which was cut and then folded into theconfiguration shown. Alternative materials and construction methods may,of course, be employed. Fan 700 was mounted to the top of shroud 600 byinserting plastic rivets in mounting holes 614. Alternative mountingmethods may be used.

Shroud 600 includes protrusions 616 on each end 608 for engagingretaining ledges 404 of retaining members 400. In addition, shroud 600also includes shoulder portions 618 which act as insertion stops whenshroud 600 is placed over the tops of the daughterboards. (Shoulderportions 618 engage the top surface of retaining members 400 to stop themovement of shroud 600 toward motherboard 502 as shroud 600 is beingplaced over the daughterboards.) Preferably, protrusions 616 should bedisposed below shoulder portions 618 by a distance that will allow themto engage the undersides of retaining ledges 404 just before shoulders618 contact the top surfaces of retaining members 404. In an embodiment,ends 608 were separated by a distance that was slightly smaller than thedistance between retaining members 400. Such a spacing was adequate toenable protrusions 616 to engage retaining ledges 404 when shroud 600was placed over the daughterboards.

Shroud 600 includes guide slots 620 on each end 608. Each of theheatsinks on the daughterboards includes end tabs 116. After thedaughterboards have been installed into their sockets on motherboard 502as shown in FIG. 9, notches 118 in end tabs 116 engage retaining ledges404 on one end of ledges 404, leaving the other end of retaining ledges404 free. Guide slots 620 are used to properly align shroud 600 overtabs 116 for installation as indicated by dashed lines 902. When slots620 are disposed over tabs 116, protrusions 616 align themselves withthe free end of retaining ledges 404. Shroud 600 is lowered intoposition until protrusions 616 engage the free end of retaining ledges404 as shown in FIG. 10. It can be seen in FIG. 10 that shoulderportions 618 on shroud ends 608 act as insertion stops when they engagethe top surfaces of retaining members 400.

Additional heat removal efficiency may be achieved by mountingdaughterboard system 500 in a host computer chassis 1100 as shown inFIG. 11. In the configuration of FIG. 11, the effluent path 1104 of fan700 is proximate to the intake path 1106 of a chassis ventilation fan1102. This enables chassis fan 1102 to direct heat-containing effluentfrom daughterboard system 500 to the exterior of chassis 1100.

First preferred heatsink. A first preferred heatsink for optional usewith daughterboard system 500 will now be described with reference toFIGS. 12-14. Heatsink 1200 was extruded using an aluminum 6063-T5material. Other materials and fabrication techniques may be used.Heatsink 1200 includes a rectangular base portion 1202 having alongitudinal dimension 1204 longer than its transverse dimension 1206.Tabs 116 were cut on either end of the base portion, for engagingretaining members 400 disposed proximate to a socket of a motherboard502. Four holes were drilled into the bottom of base portion 1202 forreceiving mounting pins 1208 for anchoring heatsink 1200 to adaughterboard. Numerous transverse fins 1210 were integrally formed withbase portion 1202 during extrusion. Fins 1210 were radially displacedfrom one another, as shown.

Base portion 1202 has end parts 1214 and a central part 1212. Centralpart 1212 is preferably disposed directly over the heat generatingcomponent(s) of the daughterboard, and is thicker than end parts 1214 toenhance heat removal effectiveness over the components. In theillustrated embodiment, the thickness of central part 1212 of baseportion 1202 varies according to an inner radius 1300 of fms 1210. Inone embodiment, inner radius 1300 was approximately 119.2 mm. Theprofile 1302 formed by the outer ends of fins 1210 varies according toan outer radius 1304. In one embodiment, outer radius 1304 wasapproximately 136.8 mm and was constant for each of fms 1210. The innerradius, however, was not constant for each of fins 1210. Specifically,inner radius 1306 (associated with the fins coupled to end parts 1214 ofbase portion 1202) was slightly longer than inner radius 1300(associated with the fins coupled to central part 1212 of base portion1202). Variation of the inner fin radius in this manner enablesadditional fins to be placed on heatsink 1200 while maintaining aconstant outer radius 1302.

Preferably, central part 1212 of base portion 1202 is adapted to becoupled to the a heat generating component of the daughterboard. In oneembodiment, this was accomplished by attaching a thermally conductivealuminum foil to the central area 1216 of the bottom of base 1202. Onematerial that was found to be useful for this purpose is sold under thetrademark THERMSTRATE, and is available from Foxcon, Inc. under the partnumber 081-0001-558.

Mounting pins 1208 are illustrated in more detail in FIG. 15. Each pin1208 has a stem 1502 with a knurled cylindrical portion 1500 on one endand a clip retaining lip 1504 on the other end. During assembly, knurledportion 1500 is pressed into the previously-drilled receiving holes onthe bottom of base 1202 of heatsink 1200 forming a friction fit. Clipretaining lips 1504 are used to secure heatsink 1200 to thedaughterboard by means of a retaining clip. Retaining clips useful forthis purpose are available from Foxcon, Inc. under the part number025-0002-960. Other means may optionally be used to secure heatsink 1200to the daughterboard.

Second preferred heatsink. A second preferred heatsink 1600 for use withdaughterboard system 500 will now be described with reference to FIGS.16-18. Heatsink 1600 was extruded using the same material as heatsink1200. Other materials and fabrication techniques may be used. Heatsink1600 includes a rectangular base portion 1602 having a longitudinaldimension 1604 longer than its transverse dimension 1606. Tabs 116 werecut on either end of the base portion, for engaging retaining members400 disposed proximate to a socket of a motherboard 502. Four holes weredrilled into the bottom of base portion 1602 for receiving mounting pins1208 for anchoring heatsink 1600 to a daughterboard. Numerous transversefms 1610 were integrally formed with base portion 1602 during extrusion.Fins 1610 are all parallel to each other and orthogonal to the bottom ofbase portion 1602.

Base portion 1602 has end parts 1614 and a central part 1612. Thecentral part 1612 is thicker than the end parts 1614 to enhance heatremoval over the heat generating components of the daughterboard. Thethickness of central part 1612 of base portion 1602 varies according toa radius 1700. Radius 1700 may be approximated by step differences inthe depths of fins 1610. For example, in the embodiment shown, fivecentral fms 1702 are the shallowest depth 1704. Two groups of fiveendmost fins 1706 have the deepest depth 1708. And fin pairs 1710, 1712have intermediate depths 1714, 1716, respectively. The profile formed bythe outer ends of fins 1710 is constant relative to the bottom of thebase portion 1602.

Like heatsink 1200, heatsink 1600 is preferably adapted to be coupled toa heat generating component of the daughterboard by attaching thermallyconductive aluminum foil to the bottom of base 1602 in central area1616. Also like heatsink 1200, pins 1208 may be used to secure heatsink1600 to the daughterboard.

While the invention has been described in detail in relation to apreferred embodiment thereof, the described embodiment has beenpresented by way of example and not by way of limitation. It will beunderstood by those skilled in the art that various changes may be madein the form and details of the described embodiment without deviatingfrom the spirit and scope of the invention as defined by the appendedclaims.

What is claimed is:
 1. A heatsink, comprising: a rectangular baseportion having its longitudinal dimension larger than its transversedimension; tabs disposed on each longitudinal end of the base portion,the tabs for engaging retaining members disposed proximate to a socketof a motherboard; at least one mounting pin for anchoring the heatsinkto a daughterboard; plural transverse fins integrally formed with thebase portion, the fins oriented parallel to one another and orthogonalto the base portion; wherein the base portion has end parts and acentral part; and wherein the thickness of the central part is greaterthan the thickness of the end parts and is constant in the transversedirection but varies according to a radius in the longitudinaldirection.
 2. A heatsink according to claim 1, wherein: the outer endsof the fins define a first plane that is substantially parallel with asecond plane defined by a bottom surface of the base portion.
 3. Aheatsink according to claim 1, wherein: a bottom surface of the centralpart of the base portion is adapted to be thermally coupled to a heatgenerating component of the daughterboard by contact engagement with theheat generating component.
 4. A heatsink according to claim 1, wherein:the at least one mounting pin is coupled to the base portion by means ofa friction fit between a knurled portion of the mounting pin and areceiving hole in the base portion.
 5. A heatsink according to claim 2,wherein: a central group of fins is disposed over the central part ofthe base portion; and the lengths of the fins in the central group varyapproximately according to the radius.
 6. A heatsink according to claim5, wherein: at least two adjacent fins in the central group have thesame length.
 7. A heatsink according to claim 5, wherein: three adjacentfins in the central group have a first length.
 8. A heatsink accordingto claim 7, wherein: two adjacent fins in the central group have asecond length different from the first length and are disposed on oneside of the three adjacent fins, and two additional adjacent fins in thecentral group have the second length and are disposed on the other sideof the three adjacent fins.
 9. A heatsink according to claim 8, wherein:two adjacent fins in the central group have a third length differentfrom the first and second lengths and are disposed on one side of thethree adjacent fins, and two additional adjacent fins in the centralgroup have the third length and are disposed on the other side of thethree adjacent fins.